Generally, a terminal must be capable of performing a cell search according to a signal received from a base station in a cellular system. In order to perform a cell search, a GSM which is a cellular system of a conventional time division multiple access (TDMA) scheme, or an IS-95, a CDMA-2000, or a W-CDMA scheme, etc., which are cellular systems using conventional code division multiple access (CDMA), are provided with a downlink.
Conventional OFDMA-based systems include digital audio broadcasting (DAB), digital video broadcasting (DVB), IEEE802.11a, and HiperLAN/2 standards. These conventional OFDMA-based systems are not cellular systems so it is difficult to perform synchronization and a cell search with a conventional structure.
A scheme for supporting the OFDMA-based cellular system using two preamble symbols has been developed at IEEE802.16e.
At the two preamble symbols, a first preamble signal is used for time synchronization and frequency synchronization with a PN code which all cells commonly use, and a second preamble signal is used for a cell search by forming a correlation between the PN codes and all the cells since a signal is broadcasted using different PN codes for the respective cells. However, with these two preamble symbols, there is a problem in that an effective period, which is used for real data at one frame, is wasted.
Meanwhile, Korean Patent Application No. 1999-57310 (Dec. 13, 1999) entitled “Cell search method in a mobile communication system” discloses a method for efficiently performing a cell search in a code division multiple access system of a third generation mobile communication system using an IMT-2000 standard.
In the mobile communication system according to the prior art, the cell search method includes selecting a number N of minimal slots having a large correlation value (or considering a terminal performance and a channel environment) from among a total of 20 minimal slots at one arbitrary slot period so as to not repeatedly calculate; calculating variables for determining the selected minimal slots; and extracting more reliable minimal slots for performing a next cell search by repeatedly accumulating the same slot periods so as to optimize an extracting method of the minimal slot periods, wherein the same slot periods have a characteristic repeated for the respective frames.
US Patent Application No. 2003/0095516A1 (Mar. 22, 2003) entitled “Cell Search device and method in a mobile communication system” discloses a cell search device and method for efficiently performing a multipath and cell search in a code division multiple access system of a third generation mobile communication system using a UMTS scheme.
In the mobile communication system according to the prior art, the cell search method includes matching slot border timing and frame border timing with that of a base station, obtaining PN code timing and ending an initial cell search; searching a first area based on the PN code timing detected at the initial cell search to perform a multipath search; and then searching a second area based on the more previously obtained PN timing rather than performing a reacquisition at a slip state in which a second area is larger than a first area; and performing an adjacent cell search by selectively using the initial cell search and the multipath search according to an amount and types of information provided from the base station. Accordingly, in the UMTS scheme, a mobile station does not use the three-step cell search of the initial cell search state but only uses an predetermined area of PN code timing at the initial cell search to rapidly accomplish a cell search.
According to the prior art, the OFDMA-based cellular system can increase the effective period for the real data at one frame by using only a preamble symbol configured as a combination of different PN codes for the respective cells and a Walsh code. However, the OFDMA-based cellular system must be capable of performing time synchronization, frequency synchronization, and cell search at one preamble.
Since the preamble is configured by different PN codes for the respective cells, system performance is decreased due to a phase delay occurred by an error of the time synchronization.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.